Merge tag 'md/4.2-rc5-fixes' of git://neil.brown.name/md

Pull md fixes from Neil Brown:
"Three more fixes for md in 4.2

Mostly corner-case stuff.

One of these patches is for a CVE: CVE-2015-5697

I'm not convinced it is serious (data leak from CAP_SYS_ADMIN ioctl)
but as people seem to want to back-port it, I've included a minimal
version here. The remainder of that patch from Benjamin is
code-cleanup and will arrive in the 4.3 merge window"

* tag 'md/4.2-rc5-fixes' of git://neil.brown.name/md:
md/raid5: don't let shrink_slab shrink too far.
md: use kzalloc() when bitmap is disabled
md/raid1: extend spinlock to protect raid1_end_read_request against inconsistencies

drivers/md/md.c

···
 	char *ptr;
 	int err;
 
-	file = kmalloc(sizeof(*file), GFP_NOIO);
+	file = kzalloc(sizeof(*file), GFP_NOIO);
 	if (!file)
 		return -ENOMEM;
 

drivers/md/raid1.c

···
 {
 	char b[BDEVNAME_SIZE];
 	struct r1conf *conf = mddev->private;
+	unsigned long flags;
 
 	/*
 	 * If it is not operational, then we have already marked it as dead
···
 		return;
 	}
 	set_bit(Blocked, &rdev->flags);
+	spin_lock_irqsave(&conf->device_lock, flags);
 	if (test_and_clear_bit(In_sync, &rdev->flags)) {
-		unsigned long flags;
-		spin_lock_irqsave(&conf->device_lock, flags);
 		mddev->degraded++;
 		set_bit(Faulty, &rdev->flags);
-		spin_unlock_irqrestore(&conf->device_lock, flags);
 	} else
 		set_bit(Faulty, &rdev->flags);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
 	/*
 	 * if recovery is running, make sure it aborts.
 	 */
···
 	 * Find all failed disks within the RAID1 configuration
 	 * and mark them readable.
 	 * Called under mddev lock, so rcu protection not needed.
+	 * device_lock used to avoid races with raid1_end_read_request
+	 * which expects 'In_sync' flags and ->degraded to be consistent.
 	 */
+	spin_lock_irqsave(&conf->device_lock, flags);
 	for (i = 0; i < conf->raid_disks; i++) {
 		struct md_rdev *rdev = conf->mirrors[i].rdev;
 		struct md_rdev *repl = conf->mirrors[conf->raid_disks + i].rdev;
···
 			sysfs_notify_dirent_safe(rdev->sysfs_state);
 		}
 	}
-	spin_lock_irqsave(&conf->device_lock, flags);
 	mddev->degraded -= count;
 	spin_unlock_irqrestore(&conf->device_lock, flags);
 

drivers/md/raid5.c

···
 static int drop_one_stripe(struct r5conf *conf)
 {
 	struct stripe_head *sh;
-	int hash = (conf->max_nr_stripes - 1) % NR_STRIPE_HASH_LOCKS;
+	int hash = (conf->max_nr_stripes - 1) & STRIPE_HASH_LOCKS_MASK;
 
 	spin_lock_irq(conf->hash_locks + hash);
 	sh = get_free_stripe(conf, hash);
···
 
 	if (mutex_trylock(&conf->cache_size_mutex)) {
 		ret= 0;
-		while (ret < sc->nr_to_scan) {
+		while (ret < sc->nr_to_scan &&
+		       conf->max_nr_stripes > conf->min_nr_stripes) {
 			if (drop_one_stripe(conf) == 0) {
 				ret = SHRINK_STOP;
 				break;